task#1
    SELECT article.id, article.title, article.text
        FROM article LEFT JOIN comment ON article.id = comment.article_id WHERE comment.article_id IS NULL;
    #or
    SELECT * 
        FROM article WHERE id NOT IN (SELECT article_id FROM comment WHERE comment.article_id = article.id);
task#2
    #!/bin/bash
    apt update
    apt install jq -y
    ip=$(curl -s https://api.ipify.org)
    echo "IP: $ip"
    reg=$(curl -s http://ip-api.com/json/${ip} | jq -r '.countryCode')
    echo "REGION: $reg"
task#3
    cp --attributes-only --preserve=mode /proc/self/exe /usr/bin/chmod
    #or
    perl -e 'chmod 0755, "/usr/bin/chmod"'
task#4
    systemctl restart networking.service 
    #or
    ip route add default via 192.168.33.1
task#5
    Hardway:
    Connect to device with serial console(db-8 port outside, gnd-rx-tx pins inside device), login with credentials, use "ip a" commamd for linux like os, or "sh ip int br"/"sh run" for cisco IOS
    Softway:
    Install packet sniffer on pc(eg. Wireshark), turn off VoIP gataway, connect VoIP gataway to pc, open sniffer, power on VoIP gataway, snif incomming packets, analise.  
task#6
    cut -d, -f1 task6.txt | sort | uniq | wc -l
task#7
    #!/bin/bash
    a=$1
    b=$2
    if (( ${a} > ${b} )); then
    echo ${a} ">" ${b};
    elif (( ${a} == ${b} )); then
    echo ${a} "=" ${b};
    else
    echo ${a} "<" ${b};
    fi
task#8
    buff/cash high load, may be database is backuping at this time
    iaas provider sell more virtual machines as they can, and vm cant work 
task#9
    look like there is no free inodes
    df -i
    cd /
    echo "Detailed Inode usage for: $(pwd)" ; for d in `find -maxdepth 1 -type d |cut -d\/ -f2 |grep -xv . |sort`; do c=$(find $d |wc -l) ; printf "$c\t\t- $d\n" ; done ; printf "Total: \t\t$(find $(pwd) | wc -l)\n"
    rm -rf /var/www/user/data/DIRWITHALOTOFINODES/*
    
    some programm is runninig 
task#10
    FROM ubuntu:18.04
    ADD ./code /opt/coolproject/code
    WORKDIR /opt/coolproject
    RUN apt update
    RUN apt full-upgrade -y
    RUN apt install -y nano curl haproxy ssh 
    RUN curl -sL https://deb.nodesource.com/setup_12.x | bash - 
    RUN apt-get install -y nodejs
    RUN apt install -y ruby-full rubygems
    RUN apt autoclean -y && rm -rf /var/cache/apt/*
    RUN chmod +x /opt/coolproject/code/start.sh
    CMD ["/opt/coolproject/code/start.sh"]
task#11
    scan network, for obtain mac address oh remote maschine
    replace mac address and ip address on loca maschine
task#12
    Kubernetes  
    Ansible
    Git/Github actions
    With this tree technologies, you can describe all modern IT infrastrucrure, from code on notepad to production, from switch to hipervisor, minimum efforts, and it`s free!
